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Demodulation and Decoding Studies of the 39-Tone MIL-STD-188-110A HF Signal

A set of algorithms has been developed to demodulate and decode the 39 tone signal, which is prevalent in the High Frequency (HF) frequency band. This signal, based on the MIL-STD-188-110A Standard, is one of several different types generated by the AN/PRC-138 Harris radio. Defence R&D Canada (DRDC) - Ottawa has two of these radios. Our work focused on the 39 tone fixed frequency mode, although the 39 tone signal is also the underlying modulation used in the AN/PRC-138's frequency hopping mode. Thus, the work described here will also be useful to anyone developing dehopping and demodulation algorithms for the AN/PRC-138 frequency hopping signal. The signals were captured by the Agilent Technologies Blackbird system in a laboratory setting. The objective of the task was to gain a detailed understanding of the sophisticated 39 tone signal and to develop software radio algorithms for demodulating and decoding the signal. The report describes the signal structure, the signal capture equipment, and the steps involved in demodulating and decoding the signal so that the transmitted messages can be read at the receiving end. The report also describes the problems encountered during the algorithm development process. Since the signal captures took place in an ideal setting and a priori information of the signal structures was used to assist in the demodulation and decoding process, the current algorithms must be modified slightly to be able to handle the more general situation. The re